Bump Magnum Cluster API to 0.27.0

Add extra tool for bumping MCAPI by simply running:

> just bump-magnum-cluster-api

Change-Id: Ifbcc00b3012d14cbf2304390d999a8e425eeb6bb
diff --git a/flake.nix b/flake.nix
index 6dcbfcd..f0e044f 100644
--- a/flake.nix
+++ b/flake.nix
@@ -19,6 +19,7 @@
               earthly
               glibcLocales
               go
+              just
               kubernetes-helm
               nixpkgs-fmt
               patchutils